The goal of this proposed research is to test hypothesis pertaining to mitochondrial DNA (mtDNA) genetics in the aftermath of recent genetic bottleneck ing two California populations of yellowfin goby, a marine fish. The hypothesis is that the ratio of single-observation (i.e., singleton) mtDNAs to total distinct mtDNA observed in a population sample, is a general indicator of recent population-genetic bottlenecking. To test, I will study and compare the mtDNA and nuclear allelic genetics of two California populations of yellowfish goby, a recent colonizer from Asia, with that of a native (control) species in California plus that of a yellowfish goby population in China. Control region sequences of about 900 pairs from 50 specimen mtDNAs, plus allele frequencies at 15 microsatellite loci, from each population in each of three years will constitute the genetic data. This new approach will potentially yield new information of importance to society on what controls genetic and species diversity over relatively short time scales by providing a way to recognize contemporary, syntopic genetic bottlenecks in natural populations.